|Publication number||US7397353 B2|
|Application number||US 11/190,404|
|Publication date||Jul 8, 2008|
|Filing date||Jul 27, 2005|
|Priority date||Aug 25, 2003|
|Also published as||EP1663675A2, EP1663675B1, EP2236320A1, EP2236320B1, US7202778, US20050046558, US20050264406, WO2005043264A2, WO2005043264A3|
|Publication number||11190404, 190404, US 7397353 B2, US 7397353B2, US-B2-7397353, US7397353 B2, US7397353B2|
|Inventors||Douglas C. Myhre, Mark J. Buenz, John A. Norlien, William G. Kunik, Wade W. Williams|
|Original Assignee||Rosemount Aerospace Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (40), Non-Patent Citations (2), Referenced by (3), Classifications (14), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a divisional of prior U.S. application Ser. No. 10/647,487, filed Aug. 25, 2003 now U.S. Pat. No. 7,202,778, which is hereby incorporated by reference.
The present invention is related to aircraft tire pressure and wheel speed sensing, in general, and more particularly to a wireless tire pressure and/or wheel speed sensing system for aircraft.
It is well known that improper inflation will cause excessive wear on tires and lead to premature replacement thereof. Keeping a tire at its manufacture's recommended inflation pressure will extend the life of the tire. This is especially important in the aircraft industry where premature replacement of aircraft tires is particularly expensive. Safety is another consideration. Taking off and landing on improperly inflated tires may lead to aircraft accidents. Accordingly, checking for proper tire pressure is a mandatory part of the preflight inspection of the aircraft.
Generally, during preflight inspection, a conventional pneumatic-mechanical pressure gauge is used manually to check the tire pressure through a valve stem. However, each time the pressure is tested with such a pressure gauge a small amount of air is released from the tire. Thus, over a number of inspections, the tire will become under inflated and will require re-inflation which is a timely and costly maintenance process. To reduce the frequency of tire re-inflation, some commercial aircraft wheels have been equipped with a fixed pneumatic coupling to the valve stem via a spinning coupler. In such a system, the monitored tire pressure is converted to an electrical signal which may be read by a hand held tire pressure reader, for example. As with any moving part, the pneumatic spinning coupler suffers from wear with time which may lead to air pressure leakage. Accordingly, maintenance is required at frequent intervals.
A more recent wheel mounted pressure monitoring system provides for a fixed pneumatic coupling without a spinning coupler. This system converts the monitored pressure into a proportional alternating or pulsed electrical signal which is passed through a pair of transformer coils which are closely coupled. One coil is stationary and the other is rotating. Such a system is considered rather bulky and expensive. In addition, the accuracy of the electrical pressure signal is vulnerable to environmental changes at the wheel which may vary in temperature from −50° C. to approximately 150° C., for example., and be exposed to inclement weather conditions as well.
The present invention provides for an aircraft wheel mounted tire pressure monitoring unit which overcomes the drawbacks of the present systems. In addition, the present invention may include wheel speed sensing with minimal additional wheel mounted components.
In accordance with one aspect of the present invention, a wireless tire pressure sensing system for an aircraft comprises: dual resonant circuits mounted to a wheel of the aircraft, one resonant circuit comprising: a first variable capacitance sensor for monitoring the pressure of a tire mounted to the wheel; and a first wire loop of a first predetermined inductance coupled to the first variable capacitance sensor, and the other resonant circuit comprising: a second variable capacitance sensor operative as a reference to the first variable capacitance sensor; and a second wire loop of a second predetermined inductance coupled to the second variable capacitance sensor; an interrogating circuit magnetically coupleable to the dual resonant circuits and operative to induce magnetically a variable frequency current in the dual resonant circuits, the one resonant circuit responding to the induced current with an E-field signal at a first resonant frequency commensurate with the capacitance of the first variable capacitance sensor, and the other resonant circuit responding to the induced current with an E-field signal at a second resonant frequency commensurate with the capacitance of the second variable capacitance sensor; a receiving circuit E-field coupleable to the dual resonant circuits and operative to receive the E-field signals at the first and second resonant frequencies and to generate first and second signals representative thereof; and a processing circuit coupled to the receiving circuit for processing the first and second signals to generate a compensated pressure reading of the tire.
In accordance with another aspect of the present invention, a method of wirelessly measuring pressure of a tire of an aircraft comprises the steps of: mounting first and second resonant circuits to a wheel of the aircraft to which the tire is mounted; monitoring tire pressure with the first resonant circuit; using the second resonant circuit as a reference to the first resonant circuit; generating a variable frequency signal; magnetically coupling the variable frequency signal to the first and second resonant circuits; inducing first and second resonant frequencies in the first and second resonant circuits, respectively, by the magnetically coupled variable frequency signal, the first resonant frequency representative of an uncompensated pressure reading and the second resonant frequency signal representative of a compensation reading; E-field coupling the first and second resonant frequencies from the first and second resonant circuits to a receiver circuit; and generating a compensated pressure reading from the E-field coupled first and second resonant frequencies.
In accordance with yet another aspect of the present invention, a wireless tire pressure and wheel speed sensing system for an aircraft comprises: a resonant circuit mounted to a wheel of the aircraft for monitoring the pressure of a tire mounted to the wheel, the resonant circuit comprising a wire loop of a predetermined inductance; an interrogating circuit magnetically coupleable to the resonant circuit and operative to induce magnetically a variable frequency current in the wire loop of the resonant circuit, the resonant circuit generating a corresponding variable frequency electric field in response to the induced current, the variable frequency electric field including a resonant frequency commensurate with the pressure of the tire; a magnetic field altering apparatus for alternating the magnetic coupling between the wire loop and the interrogating circuit to cause a rate of amplitude modulations of the variable frequency electric field commensurate with the wheel speed; a receiving circuit E-field coupleable to the resonant circuit and operative to receive the amplitude modulated variable frequency electric field of the resonant circuit and to generate a signal representative thereof; a first processing circuit coupled to the receiving circuit for processing the signal to generate a pressure reading of the tire based on the resonant frequency thereof; and a second processing circuit coupled to the receiving circuit for processing the signal to generate a wheel speed reading based on the rate of amplitude modulations thereof.
In accordance with a further another aspect of the present invention, a wireless tire pressure sensing system for an aircraft comprises: a resonant circuit mounted to a wheel of the aircraft, the resonant circuit comprising: a variable capacitance sensor for monitoring the pressure of a tire mounted to the wheel; and a wire loop of a predetermined inductance coupled to the variable capacitance sensor; an interrogating circuit magnetically coupleable to the resonant circuit and operative to induce magnetically a variable frequency current in the resonant circuit, the resonant circuit responding to the induced current with an E-field signal at a resonant frequency commensurate with the capacitance of the variable capacitance sensor; a receiving circuit E-field coupleable to the resonant circuit and operative to receive the E-field signal at the resonant frequency and to generate a signal representative thereof; and a processing circuit coupled to the receiving circuit for processing the signal to generate a pressure reading of the tire.
In accordance with a still further aspect of the present invention, a method of wirelessly measuring pressure of a tire of an aircraft comprises the steps of: mounting a resonant circuit to a wheel of the aircraft to which the tire is mounted; monitoring tire pressure with the resonant circuit; generating a variable frequency signal; magnetically coupling the variable frequency signal to the resonant circuit; inducing a resonant frequency in the resonant circuit by the magnetically coupled variable frequency signal, the resonant frequency representative of a pressure reading; E-field coupling the resonant frequency from the resonant circuit to a receiver circuit; and generating a pressure reading from the E-field coupled resonant frequency.
In accordance with a still further aspect of the present invention, a wireless wheel speed sensing system for an aircraft comprises: a wire loop mounted to a wheel of the aircraft and rotating therewith; an interrogating circuit magnetically coupleable to the rotating wire loop and operative to induce magnetically a current signal in the rotating wire loop, the rotating wire loop generating a corresponding electric field in response to the induced current; a magnetic field altering apparatus for alternating the magnetic coupling between the wire loop and the interrogating circuit to cause a rate of amplitude modulations of the electric field commensurate with the wheel speed; and a receiving circuit statically mounted with respect to the rotating wheel, the receiving circuit operative to receive the amplitude modulated electric field and to generate a signal representative of wheel speed.
An embodiment of the wireless tire pressure sensing system in accordance with one aspect of the present invention comprises two parts. One part is made up of dual, aircraft wheel mounted, resonant circuits. One of the dual resonant circuits varies in resonant frequency as tire pressure, temperature and other parameters vary and the other or reference resonant circuit varies in resonant frequency only with temperature and other parameter variations. The second part of the system is an aircraft landing gear mounted or handheld exciter unit that generates a variable frequency magnetic field to excite the wheel mounted pressure and reference resonant circuits and determines the resonant frequencies thereof as will become better understood from the description below.
In the present embodiment, each resonant circuit comprises an inductor, which is formed by a loop of wire of conductive material, like copper, for example, and a variable capacitor sensor configured in a tank circuit. The copper wire loop, which also acts as an antenna for its respective resonant circuit, may be mounted to a layer of temperature stable material, like a PC card, for example, which is supported by a support structure within a hub or hubcap of the wheel. The size of a supporting structure for the dual, inductive wire loops is dependent on the width and diameter of the hubcap of the aircraft on which it is to be mounted. Generally, the smallest tire dimensions correspond to the nose wheel of the aircraft. The construction of the hubcap mounted inductive wire loop assembly will be described in greater detail herein below. Testing of the dual resonant circuits for frequency response, range of activation, effects of capacitance on frequency, and frequency response changes that occur with changes in shape (bending) of the supporting structure revealed that the reference resonant circuit mounted on the same assembly as the tire pressure measuring resonant circuit will eliminate substantially the frequency variations on the pressure measurement that come with mounting variations, environmental factors and temperature changes.
A block diagram schematic illustration of the embodiment of the wireless tire pressure sensing system is shown in
The exciter or interrogator circuit 14 includes a sweep frequency oscillator 18 and a responsor receiver 20 both integrated into a phase lock loop (PLL) 22. Circuit 14 further includes a magnetic interrogator unit 24 comprising a coil of wire 26 wound around a ferrite core 28. For each pressure measurement, the oscillator 18 generates a frequency signal in the RF range to drive the coil 26 which causes the interrogator 24 to generate a magnetic field illustrated by the flux lines 30 with a swept frequency which may vary from about fourteen MHz to approximately twenty MHz, for example. Whether embodied in a hand held reader or a landing gear mounted unit, the exciter circuit 14 is disposed in proximity to the dual, resonant circuits such that the lines of flux 30 on the magnetic interrogator 24 will induce current in the inductive loops 12. The inductive loops 12 are each commonly E-field coupled to a receiving E-field loop antenna 32 to, in turn, induce current in the loop antenna 32 which is measured by a sensing circuit 34 which may be a wide bandwidth operational amplifier, for example. To avoid H-field coupling between the interrogator 24 and the E-field loop antenna 32, the loop antenna 32 is designed to receive RF signals in the E-field null range of the magnetic interrogator 24. A signal representative of the loop current measured by sensing circuit 34 is conducted over signal lines 36 to the responsor receiver 20 and coupled to the PLL 22. It is understood that the sensing circuit 34 may be also embodied in the unit 14, in which case, wires 36 carry the signal of antenna loop 32 to the unit 14 for sensing therein.
Resonance of each respective resonant circuit 10 is dependent on the capacitance of the respective capacitor sensor 16. Accordingly, during a pressure measurement, as the sweep frequency approaches resonance of each resonant circuit 10, the amplitude of the induced current in loop 32 peaks. As will become more evident from the following description, during the pressure measurement frequency sweep as exemplified in the graph of
In a handheld interrogator version which is depicted by the block diagram schematic of
A landing gear mounted embodiment of the one aspect of the present invention is shown in the simplified illustration of
A block diagram schematic of circuitry suitable for embodying the circuits 18, 20 and 22 enclosed in the enclosure 54 is shown in
In operation, the processing unit 100 may be maintained in a power saving sleep mode until it receives the start measurement signal 122. Then, under program control, the processing unit 100 provides the start signal 102 and start frequency 104 to the frequency generator 108. The phase lock loop is designed in the present embodiment such that the starting frequency generated by circuit 106 is out of phase from the anticipated resonance frequency of the system. The phase comparator circuit 112 compares the phase of the generated frequency over line 114 with the frequency of the received E-field signal (output of amplifier 116). The phase error signal 118 of the comparator circuit 112 causes the frequency generator to continue to sweep across a frequency range from the start frequency until the phase error signal goes to zero which is indicative of frequency lock condition. In the present embodiment, from start to lock may take less than one millisecond. Under frequency lock, the frequency generator 106 dwells at the first resonance frequency 38 as shown in
At frequency lock, the lock signal 120 provided to the processing unit 100 causes the unit 100 to execute a program to determine the first resonance frequency from the pulsed signals over line 110. For example, under program control, the unit 100 may count the number of pulses in a counter register over a predetermined period, like on the order of one second, for example. The total count from the counter indicative of the first resonance frequency may be stored in a temporary register of the unit 100. Thereafter, the unit 100 may be programmed to provide a new start frequency beyond the first resonance frequency over lines 104 and another start signal over line 102. In response, the frequency generator 106 generates a signal over lines 108 at the new start frequency which is by design out of phase with the next resonance frequency. The non-zero phase error signal 118 of the comparator circuit 112 causes the frequency generator to continue to sweep across a frequency range from the new start frequency until the phase error signal goes to zero again indicative of the second frequency lock condition. Under frequency lock, the frequency generator 106 dwells at the second resonance frequency 40 as shown in
The processing unit 100 may be also programmed to compare the compensated tire pressure measurement to a predetermined pressure and control a non-volatile indicator 126 over signal line 128 to different states based on the outcome of the comparison, i.e. whether the compensated tire pressure measurement is above or below the predetermined pressure.
A cross-sectional illustration of an integrated aircraft wheel assembly 200 suitable for embodying the principles of the present invention is shown in
The central structure 208 protrudes through the centers of the annular shaped layers 212 and 214 to the surface 210 of the hubcap 202. The magnetic interrogator 24 is disposed on the central structure 208 at a point near the surface 210 in close proximity to the dual loops 10 of layer(s) 212 so that its magnetic field is directed to induce a current in the dual loops 12 while not affecting substantially the E-field receiving loop 32. Wires 26 may extend from the landing gear strut mounted unit 54 through the center of axle 206 to the magnetic interrogator 24. Likewise, wires 36 may extend from the receiving loop 32 of PC board layer 214 through the center of axle 206 to the strut mounted unit 54 as described herein above in connection with
In the present embodiment, dual, variable capacitance pressure sensors 16 are disposed in a common enclosure, like a TO-5 can, for example, of a sensor assembly 216. A hollow metal tube 218 is attached to the base of the TO-5 can of assembly 216 and is insertable into a cavity 220 of the wheel rim 204 at an insertion point 222. The cavity 220 extends from the insertion point 222 up through the rim 204 to the tire pressure chamber (not shown). A hole (not shown) is provided in the base of the TO-5 can at a point where the tube 218 is attached so that pressure from the tire chamber may be sensed by a pressure sensor in the assembly 216 via the path through cavity 220, tube 218 and the hole in the base of the assembly 216 as will become more evident from the description found herein below. A seal 223 may be included around the tube 218 at the insertion point 222 to ensure against air leakage from the cavity 220 to the atmosphere. Wiring from the dual pressure sensors of assembly 216 may be provided to their respective inductor loops in the hubcap 202 through a cable 224, which may be a coax cable, for example, and a connector 226, which may be a coax connector. The connector 226 is disposed through a wall of the hubcap 202 to permit the wiring thereof to pass through the wall and be connected to their respective loops on PC board layer(s) 212.
In addition, wire circles 238 may be provided on surface 234 at a point 240 of loop 232 to increase the length and inductance of the loop 232 to provide an inductance range around the contemplated operational resonance frequency of the respective resonant circuit. Trimming the inductance to compensate for variations in the manufacturing process may be accomplished with the present embodiment by cutting or interrupting the connection of one or more of the wire circles from the wire loop 232, for example. In this manner, once trimmed, there is no further need to calibrate the resonant circuits, allowing the wheels to be changed with no adjustment in the exciter unit.
Contacts to the aforementioned plates of the capacitive element of each MEMS sensor 250 and 252 are provided at 290 and wire leads 292 and 294 may be connected to each contact for connecting the capacitive plates to pins 296 and 298 which penetrate the base 258 for external sensor connections. Profile, top and isometric illustrations of the TO-5 can 254 of the dual sensor assembly are shown in
Accordingly, air pressure from the tire chamber is sensed in chamber 268 of sensor 252 via the path formed by cavity 220, tube 218, hole 262, hollow pedestal portion 264, and substrate pathway 270. Pressure in chamber 268 causes the capacitive plate of diaphragm 266 to move with respect to the capacitive plate of stationary substrate 256, thus varying the capacitance in proportion to the sensed pressure. The capacitance of sensor 252 will also vary with changing temperature and other parameters. Since sensor 250 is not sensing tire pressure, the capacitance thereof will only vary with the changing temperature and other parameters which are substantially the same for both sensors. In addition, the inductor loops of the dual resonant circuits are fixed and temperature stabilized for the most part. Any variation in inductance of the dual loops due to the changing temperature and other parameters will be substantially the same for both loops. Accordingly, the resonant frequency of the reference LC circuit may be used to compensate the resonant frequency of the pressure measuring LC circuit by taking the differential resonant frequency between the two as described herein above in connection with
In addition to tire pressure, wheel speed may be also sensed wirelessly by the foregoing described embodiment(s) with a minor modification and/or addition of one or more components. The basic concept of wireless wheel speed sensing utilizing the present tire pressure sensing embodiment(s) is to cause a rate of amplitude modulations of the variable frequency magnetic field between the rotational and static loop circuits commensurate with the wheel speed. One technique for creating the rate of amplitude modulations is to provide breaks or interruptions, i.e. inductive discontinuities, in the magnetic coupling between the interrogator 24 and resonant loop 10. The illustration of
In the embodiment of
To provide additional structural support to the gratings 322, if needed, a circular ring 326 may couple together the unattached ends of the gratings 322. The center hole of the ring 326 is aligned substantially with the center hole of the layer 212. The outer diameter of the circular ring 326 is less than the diameter of the inductive loop 10, but the gratings 322 extend over the loop 10 to act as barriers or shields to the magnetic field between the magnetic interrogator 24 and the loop 10. The ring 326 is also electrically grounded through its contact with the grounded gratings 322.
Since the gratings 322 are attached to the layer 212 which is affixed to the wheel hub, they will rotate with the wheel. Accordingly, the variable frequency E-field signal received over signal lines 36 will have a rate of amplitude modulations commensurate with wheel rotational speed as illustrated in the exemplary waveform of
If the gratings 322 do not provide a desired amplitude modulation of the variable frequency signal, then a second set of gratings aligned concentric to the first may be added to the embodiment of
While the present embodiment employs a rotating plurality of gratings 322 or a rotating and static set of gratings as described above to achieve the desired amplitude modulations, it is understood that other embodiments or even other shuttering mechanisms may be employed without deviating from the broad principles of the present aspect of the invention. Such other shuttering mechanisms may take the form of holes or apertures in a disc attached above the loop 10 or a combination of fixed and a static holed discs as described above. Wired spokes that act as RF magnetic shields may be used instead of gratings to provide the desired modulations in the RF throughput.
Another possible technique to sensitize the magnetic field to wheel rotation is to alter the shapes of the transponder and receiver loops. By changing the shape of the transmitting and receiving loops the distance between the two loops 10 and 32 varies as the wheel rotates. The science of Physics dictates that the transmitting of electromagnetic radiation will vary with the inverse of the square of the distance between the loops 10 and 32. Therefore, as this distance varies with rotation, the E-field signal will be amplitude modulated commensurate with wheel speed.
A modified system suitable for embodying this principle is shown by the illustration of
It is understood that while the present embodiment shapes the wire loops into multiple pointed stars to achieve the desired amplitude modulations, other shapes of the wire loops are possible without deviating from the broad principles of the present aspect of the invention. Such other shapes may take the form of square waves or sine waves or any shape that varies radially or axially in a regular pattern, for example.
Another possible technique to effect the desired amplitude modulation for wireless wheel speed sensing is to locate ferro-magnetic material relative to the magnetic interrogator 24 and transponder loop 10 in order to enhance or detract the magnetic coupling therebetween. The use of ferrite material embedded in the insulated layer 212 at regular intervals and in close proximity to the transmitting loop 10 will create a distortion of the RF magnetic waves, resulting in a deviation in the characteristic of the magnetic flux lines intersecting the transmitting loop 10 and, in turn, a fluctuation in the E-field signal as the wheel rotates. This technique may be also used in the same or similar manner as described herein above for the grating embodiment of
While the present invention has been described herein above in connection with one or more embodiments, it is understood that these descriptions are provided merely by way of example. Accordingly, the present invention should not be limited in any way by such description, but rather construed in breadth and broad scope in accordance with the recitation of the claims appended hereto.
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|U.S. Classification||340/448, 340/447, 340/444, 73/146.5|
|International Classification||B60C23/04, B60C23/00|
|Cooperative Classification||G01P3/44, B60C23/0428, G01P3/48, B60C23/043|
|European Classification||B60C23/04C6C1, B60C23/04C6C2, G01P3/48, G01P3/44|
|Aug 29, 2005||AS||Assignment|
Owner name: ROSEMOUNT AEROSPACE INC., MINNESOTA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MYHRE, DOUGLAS C.;BUENZ, MARK J.;NORLIEN, JOHN A.;AND OTHERS;REEL/FRAME:016677/0606
Effective date: 20050718
|Jan 9, 2012||FPAY||Fee payment|
Year of fee payment: 4